The present invention relates to a commutator connected to an armature at one end and having a noise-preventing electric element at the other end.
To connect a noise-preventing electric element such as a varistor, a resistance and a thick-film integrated circuit to a commutator in a compact direct current motor, a connecting electrode of an annular noise-preventing electric element is soldered to a connecting portion between a coil and a commutator segment.
For example, the commutator is mounted to an armature in which the coils are applied around an iron core. The windings such as coils are connected to a coil connecting portion of the commutator segment, and the annular noise-preventing electric element is connected to the coil connecting portion of the commutator segment.
A connecting portion between the commutator segment and the coil of the armature is located between the commutator and the coil, and an annular noise-preventing electric element is made such that its diameter is larger than the outer diameter of the commutator. To solder the noise-preventing electric element on a coil-connecting terminal of the commutator, it is necessary to increase the inner diameter of the element.
The terminal of the commutator segment is connected to the connecting electrode of the noise-preventing electric element by soldering electrically and mechanically.
In the above method of connecting the commutator segment to the annular noise-preventing electric element, the internal diameter of the element increases to facilitate assembling, and reduction in precision of the element improves yield. So distance between the electrodes to be soldered increases to lose weight balance to cause vibration.
Further in use the soldered portion is liable to come off by vibration and it is thus preferable to bridge soldering to a spaced portion. The soldering material contains a lot of lead as heavy metal to cause environmental pollution. It is preferable to avoid such use.
To increase bonding performance of the soldering material, resin flux often requires washing of the flux after soldering. Washing requires a lot of organic solvents which are liable to cause environmental pollution, and they should be avoided.
Increase in the number of slots in the commutator increases the number of the commutator segments and the steps of soldering.
Increase in the number of slots increases soldered portions, and unbalance in the soldered amount leads unbalance in rotation mass balance of the armature to cause vibration.
When an armature in which the annular noise-preventing electric element and commutator are soldered is used in high temperature, soldering is melted and scattered to the environment by centrifugal force of the armature, which is dangerous. When high melting point soldering is made, unbalanced thermal impact is applied to sintered low-conduction varistors as noise-preventing electric element in soldering to cause cracking.
Further, difference in thermal capacity between the commutator segment and the noise-preventing electric element requires preheating step of the commutator to make soldering rapidly, but the preheating step involves low thermal efficiency to consume excessive heat energy and increase manufacturing cost.